[css-sizing-4] Define some reasonable handling for aspect ratios and intrinsic heights.

Author: fantasai

css-sizing-4/Overview.bs

@@ -101,8 +101,6 @@ Intrinsic Aspect Ratios: the 'aspect-ratio' property</h3>
 	at least one of these sizes must be ''width/auto''
 	for the aspect ratio to have an impact on sizing.
 
-	ISSUE: Clarify interaction with intrinsic size keywords like ''width/min-content'' etc.
-
 	<div class="example">
 		This example sets each item in the grid to render as a square,
 		determining the number of items and their widths by the available space.
@@ -155,6 +153,37 @@ Intrinsic Aspect Ratios: the 'aspect-ratio' property</h3>
 		This would avoid the need for extra reflows after loading.
 	</div>
 
+	On non-replaced elements with an ''width/auto'' <a>inline size</a>
+	(or any replaced element whose intrinsic <a>block size</a>
+	depends on its <a>inline size</a>),
+	the intrinsic <a>block sizes</a> of the box
+	are assumed to be zero
+	when applying 'min-block-size' to the aspect ratio calculations,
+	and assumed to be infinity
+	when applying 'max-block-size' to the aspect ratio calculations.
+	These limits take effect as usual for non-replaced elements
+	once the <a>inline size</a> is resolved.
+
+	<div class="example">
+		For example, given a (<a>horizontal writing mode</a>) element with
+		<pre>
+		  width: auto;
+		  min-height: min-content;
+		  aspect-ratio: 1/1;
+		</pre>
+
+		using the aspect ratio to resolve the width
+		would require knowing the min-content height of the element.
+
+		Since for a non-replaced element,
+		this value is not known until the width is resolved,
+		we assume the 'min-height' value is zero
+		while resolving the width.
+
+		Then, once the width is known, we resolve the height,
+		taking into account the ''height/min-content'' minimum.
+	</div>
+
 <h3 id="from-ratio">
 Aspect Ratio Limits Option A: the ''from-ratio''</h3>